Telephone transmitter



March 27, 1934.

FIG.

L. c. POCO'CK El AL 52,889

TELEIHONE TRANSMITTER Filed Jan. 6 1931 x 4 9 I4 k? r Q i 6741117 & 4M

ATTORNEY Patented Mar. 27, 1934 UNITED STATES PATENT OFFICE TELEPHONE TRANSMITTER Application January 6, 1931, Serial No. 506,890 In Great Britain February 21, 1930 6 Claims. (01. 179-122) This invention relates to telephone transmitters and more particularly to telephone transmitters of the kind comprising a movable member or diaphragm and a granule chamber.

The chief object of the invention is the production of a transmitter which is of simple construction and which is extremely sensitive and faithful in'reproducing speech sounds.

According to the main feature of the invention,

a transmitter of the granular type is provided in which one electrode is fixed while the walls of the chamber containing the carbon granules move with the diaphragm. Preferably the granule chamberis made of a light flexible material such as silk or cellulose acetate. i

Figs. 1 and 2 of the accompanying drawing illustrate two embodiments of our invention both figures consisting of sectional elevations.

In the embodiment shown in Fig. 1 the transmitter diaphragm 1 which is of conical shape is preferably made of duralumin or other light metal or alloy and is stiffened at the .center by radial ribs or corrugations 2.

The granule chamber 3 which is substantially cylindrical in shape is made of a light and flexible material such as silk, cellulose acetate or the like and connected to the diaphragm 1. Preferably the walls are stiif while the rear end is flexible. If desired, the walls maybe provided with a lining of paper or the like. The front end -of the granule chamber 315 formed with a rim which is preferably attached to the inside surface of the diaphragm 1, around an aperture 5 formed therein, by a fixing solution, such as cellulose acetate, for connecting the granule chamber with the diaphragm and the granule chamber may be provided with a paper lining.

The-front electrode 4 consists of a thin metal cup, and the inner surface of this cup which makes contact with the granules in'the chamber 3, is plated with a conducting material, such .as gold, for preventing corrosion. The cup portion of the electrode 4 is adapted to be pushed into a 5 central aperture 5 in the diaphragm 1 after the granules have been inserted in the chamber 3 and is secured in position by a plurality of tongues 6 which project through holes 7 in the diaphragm and are bent over an aluminum collar or annulus 8 which acts as an additional securing means for the chamber 3. The back electrode 9, which is made of suitable material such as brass, plated upon its exposed surface in a similar manner to the front electrode is mounted within the 5 granule chamber and is formed with a threaded brane 22 is inserted over the diaphragm 1 and extension or stem 10 which projects through a hole in the back of the granule chamber 3.

The transmitter diaphragm and granule chamher are assembled by first mounting the back electrode within the granule chamber which is then secured to the diaphragm in the mannerdescribed above, the granules then being inserted in the granule chamber and the detachable front electrode subsequently inserted into the aperture in the diaphragm.

A conical brass transmitter casing 11 houses the diaphragm 1 and the granule chamber 3, the diaphragm being held between two clamping rings 12 and 13 and the back electrode 9 being rigidly secured on the transmitter casing 11 in a manner which will now be described.

An insulating spacing washer 14 is first threaded on the electrode stem 10 to allow for movement of the granule chamber with the diaphragm when the transmitter has been assembled, and a. further washer 15 of insulating material is then. forced on the stem which is knurled. or scored at this part to prevent this washer from turning pn it. The washer 15 is provided with two slots or openings 16, which are made to register with a pair of diametrically opposite tongues 17 pressed out of the casing 11, when the stem 10 is passed through the hole 18 in the backof the casing. The hole 18 is of such diameter that the stem 10 does not make contact with the casing.

An insulating washer 19 is inserted over. the stem 10 projecting through the casing 11 and the back electrode is rigidly secured on the casing 11 by tightening up a brass fixing nut 20. It will be seen that the washer 15 in cooperation with the tongues 17 serves the double purpose of preventing the electrode 9 turning when the, nut 20 is tightened and of-holding the stem 10' in a central position with respect to the hole 18 in the casing.

A pile of paper rings 21 may be inserted between the diaphragm and the casing near the edge of the diaphragm for damping the latter.

A cellulose acetate or other protective mema brass cover 23, pierced with sound apertures is placed over the whole, its edge being spun over to hold thediaphragm between the clamping rings 12, 13.

In the modification shown in Fig. 2 the arrangement is such that the flexible granule chamber 3 and the back electrode 9 are assembled on the diaphragm 1 before it is inserted in the casing 11, but that the granular carbon charge is inserted and the front electrode 4 is Ill.

pushed into the aperture in the diaphragm after the latter has been assembled in the casing.

A sleeve 24 of insulating material and a metal washer 25 are placed over the stem 10 of the back electrode 24 the end of which is then spun over to form a rigid assembly. The insulated sleeve 24 forms a close fit in the external sleeve formed in the casing 11, the wall of this external sleeve being punched in at one or more points to secure the insulated sleeve 24 in position on the casing 11. Alternatively the back electrode and the sleeve 24 may be adjustably secured by means of a locking screw passing through the wall of the casing 11.

The front electrode 4 is pushed into the diaphragm 1 after the latter has been assembled in the casing 11 and after the carbon granules have been inserted in the chamber 3. A shoulder 26 is formed on the casing 11 behind the diaphragm and adjacent the junction of the chamber 3 with it in order to provide a supI Ort for the diaphragm when the electrode 4 is pressed in position.

projecting from The electrode 4 may be secured to the diaphragm 1 by cellulose acetate or other fixing solution and it may be firmly held by tongues a collar situated on the other side of the diaphragm, the tongues passing through slots in the diaphragm and being bent down over theedge of the front electrode.

Other modifications will readily suggest themselves. For example, the diaphragm may be formed without a central aperture and the front electrode secured to its rear side by spot welding it through holes in the diaphragm to a thin ring on the outside of the latter.

, What is claimed is:

1. A telephone transm'tter of the granule typecomprising a casing, a diaphragm having a central aperture, a member of flexible materialdefining a wall of a granule chamber mounted on said diaphragm and surrounding said aperture, a back electrode mounted within said chamber and fixed to said casing, and a front electrode mounted on said diaphragm within said aperture for closing said granule chamber.

2. A telephone transmitter comprising a dia-n and a member phragm, a stationary electrode,

, granule chamber with said electrodes, said member including a stifi cylindrical portion extending between said electrodes and secured to said diaphragm and a flexible portion adjacent said second electrode and extending between said electrode and said cylindrical portion at an angle to the axis, of said cylindrical portion.

4. A telephone transmitter comprising a conical diaphragm, an electrode mounted on said diaphragm and movable therewith,- a stationary electrode in juxtaposition to said movable electrode, a member of thin flexible material encircling. said electrodes and defining a granule chamber therewith, said member being secured to said diaphragm, and means for reinforcing the major portion of said member.

5. A telephone transmitter comprising a desing, an electrode aflixed to said casing, a diaphragm mounted insaid casing, said diaphragm having an aperture in alignment with said-electrode, a hollow cup-shaped member, the base portion of which is secured between said casing and said electrode, defining a granule chamber in communication with said aperture, and an electrode extending into said chamber and closing said aperture.

'6. A transmitter comprising a casing, a diaphragm, an electrode forming part of said diaphragm, a stationary electrode and a hollow member of flexible material having a paperlined portion attached to said diaphragm at one end and having a flexible portion connecting said lined portion to, the stationary electrode, said electrodes and said hollow member defining a carbon granule chamber.

LYNDALL CROSSTHWAITE POCOCK. CHRISTOPHER BERNARD VERE NEILSON. REGINALD BLACKBURN. 

